Filler-fiber composite

ABSTRACT

The present invention relates to a filler-fiber composite, a process for its production, the use of such in the manufacture of paper or paperboard products and to paper produced therefrom. More particularly the invention relates to a filler-fiber composite in which the morphology and particle size of the mineral filler are established prior to the development of the bond to the fiber. Even more particularly, the present invention relates to a PCC filler-fiber composite, wherein the desired optical and physical properties of the paper produced therefrom are realized.

FIELD OF THE INVENTION

[0001] The present invention relates to a filler-fiber composite, aprocess for its production, the use of such in the manufacture of paperor paperboard products and to paper produced therefrom. Moreparticularly the invention relates to a filler-fiber composite in whichthe morphology and particle size of the mineral filler are establishedprior to the development of the bond to the fiber. Even moreparticularly, the present invention relates to a PCC filler-fibercomposite, wherein the desired optical and physical properties of thepaper produced therefrom are realized.

BACKGROUND OF THE INVENTION

[0002] Loading particulate fillers such as calcium carbonate, talc andclay on fibers for the subsequent manufacture of paper and paperproducts continues to be a challenge. A number of methods, having somedegree of success, have been used to address this issue. To insure thatfillers remain with or within the fiber web, retention aids have beenused, direct precipitation onto the fibers have been used, a method toattach the filler directly to the surface of the fiber have been used,mixing the fiber and the filler have been used, precipitation withinnever dried pulp have been used, a method for filling the cellulosicfiber have been used, high shear mixing have been used, fiberousmaterial and calcium carbonate have been reacted with carbon dioxide ina closed pressurized container, fillers have been trapped by mechanicalbonding, cationically charged polymers have been used and pulp fiberlumen loaded with calcium carbonate have all been used to retain fillerin fiber for subsequent use in paper. Most of the methods for fiberretention are both expensive and ineffective.

[0003] Therefore, what is needed is a filler fiber composite and amethod for producing the same that is both effective in retaining thefiller and inexpensive for the paper maker to utilize.

[0004] Therefore, an object of the present invention is to produce afiller-fiber composite. Another object of the present invention is toprovide a method for producing a filler-fiber composite. While anotherobject of the present invention is to produce a filler-fiber compositethat maintains physical properties such as tensile strength, breakinglength and internal bond strength. Still a further object of the presentinvention is to produce a filler-fiber composite that maintains opticalproperties such as ISO opacity and pigment scatter. While still afurther object of the present invention is to provide a filler-fibercomposite that is particularly useful in paper and paperboard products.

RELATED ART

[0005] U.S. Pat. No. 6,156,118 teaches mixing a calcium carbonate fillerwith noil fibers in a size of P50 or finer.

[0006] U.S. Pat. No. 5,096,539 teaches in-situ precipitation of aninorganic filler with never dried pulp.

[0007] U.S. Pat. No. 5,223,090 teaches a method for loading cellulosicfiber using high shear mixing of crumb pulp during carbon dioxidereaction.

[0008] U.S. Pat. No. 5,665,205 teaches a method for combining a fiberpulp slurry and an alkaline salt slurry in the contact zone of a reactorand immediately contacting the slurry with carbon dioxide and mixing soas to precipitate filler onto secondary pulp fibers.

[0009] U.S. Pat. No. 5,679,220 teaches a continuous process for in-situdeposition of fillers in papermaking fibers in a flow stream in whichshear is applied to the gaseous phase to complete the conversion ofcalcium hydroxide to calcium carbonate immediately.

[0010] U.S. Pat. No. 5,122,230 teaches process for modifying hydrophilicfibers with a substantially water insoluble inorganic substance in-situprecipitation.

[0011] U.S. Pat. No. 5,733,461 teaches a method for recovery and use offines present in a waste water stream produced in a paper manufacturingprocess.

[0012] U.S. Pat. No. 5,731,080 teaches in-situ precipitation wherein themajority of a calcium carbonate trap the microfiber by reliable andnon-reliable mechanical bonding without binders or retention aids.

[0013] U.S. Pat. No. 5,928,470 teaches method of making metal oxide ormetal hydroxide-modified cellulosic pulp.

[0014] U.S. Pat. No. 6,235,150 teaches a method of producing a pulpfiber lumen loaded with calcium carbonate having a particle size of 0.4microns to 1.5 microns.

[0015] The problem of insuring that filler materials, such as calciumcarbonate, ground calcium carbonate, clay and talc, remain within fibersthat are ultimately to be used in paper has been subjected to a numberof proofs. However, none of the prior related art discloses a fillerfiber composite where the morphology of the filler is predeterminedprior to introducing fibers, a method for its production nor its use inpaper or paper products.

SUMMARY OF THE INVENTION

[0016] The present invention relates to a filler-fiber compositeincluding feeding slake containing seed to a first stage reactor,reacting the slake containing seed in the first stage reactor in thepresence of carbon dioxide to produce a first partially convertedcalcium hydroxide calcium carbonate slurry, reacting the first partiallyconverted calcium hydroxide calcium carbonate slurry in a second stagereactor in the presence of carbon dioxide to produce a second partiallyconverted calcium hydroxide calcium carbonate slurry and reacting thesecond partially converted calcium hydroxide calcium carbonate slurry ina third stage reactor in the presence of carbon dioxide and fibers toproduce a filler-fiber composite.

[0017] In another aspect, the present invention relates to afiller-fiber composite including feeding slake containing seed to afirst stage reactor, reacting the slake containing seed in the firststage reactor in the presence of carbon dioxide to produce a firstpartially converted calcium hydroxide calcium carbonate slurry andreacting the first partially converted calcium carbonate slurry in asecond stage reactor in the presence of carbon dioxide and fibers toproduce a filler-fiber composite.

[0018] In a further aspect, the present invention relates to afiller-fiber composite including feeding slake containing citric acid toa first stage reactor, reacting the slake containing citric acid in thefirst stage reactor in the presence of carbon dioxide to produce a firstpartially converted calcium hydroxide calcium carbonate slurry, reactingthe first partially converted calcium hydroxide calcium carbonate slurryin a second stage reactor in the presence of carbon dioxide to produce asecond partially converted calcium hydroxide calcium carbonate slurry,and reacting the second partially converted calcium hydroxide calciumcarbonate slurry in a third stage reactor in the presence of carbondioxide and fibers to produce a filler-fiber composite.

[0019] In yet a further aspect, the present invention relates to afiller-fiber composite Including feeding slake containing citric acid toa first stage reactor, reacting the slake containing citric acid in thefirst stage reactor in the presence of carbon dioxide to produce a firstpartially converted calcium hydroxide calcium carbonate slurry, taking afirst portion of the partially converted calcium hydroxide calciumcarbonate slurry adding fibers and reacting such in a second stagereactor in the presence of carbon dioxide to produce a calciumcarbonate\fiber composite to serve as a heel and taking a second portionof the partially converted calcium hydroxide calcium carbonate slurryadding fibers and surfactant and reacting in the presence of CO₂ toproduce a second partially converted Ca(OH)₂/CaCO₃/fiber material andreacting the second partially converted Ca(OH)₂/CaCO₃/fiber material inthe presence of CO₂ in a third stage reactor to produce a filler-fibercomposite.

[0020] In still a further aspect, the present invention relates to afiller-fiber composite including feeding slake containing citric acid toa first stage reactor, reacting the slake containing citric acid in thefirst stage reactor in the presence of carbon dioxide to produce a firstpartially converted calcium hydroxide calcium carbonate slurry, taking afirst portion of the partially converted calcium hydroxide calciumcarbonate slurry adding fibers and reacting such in a second stagereactor in the presence of carbon dioxide to produce a calciumcarbonate/fiber composite to serve as a heel and taking a second portionof the partially converted calcium hydroxide calcium carbonate slurryadding fibers and polyacrylamide and reacting in the presence of CO₂ toproduce a second partially converted Ca(OH)₂/CaCO₃/fiber material andreacting the second partially converted Ca(OH)₂/CaCO₃/fiber material inthe presence of CO₂ in a third stage reactor to produce a filler-fibercomposite.

[0021] In a final aspect, the present invention relates to afiller-fiber composite including feeding slake containing citric acid toa first stage reactor, reacting the slake containing citric acid in thefirst stage reactor in the presence of carbon dioxide to produce a CaCO₃heel and adding slake containing sodium carbonate to the heel materialof the first stage reactor in the presence of CO₂ to produce a partiallyconverted calcium hydroxide calcium carbonate slurry and reacting thepartially converted calcium hydroxide calcium carbonate slurry in asecond stage reactor in the presence of carbon dioxide and fibers toproduce a filler-fiber composite.

[0022] Fiber as used in the present invention is defined as fiberproduced by refining (any pulp refiner known in the pulp processingindustry) cellulose and/or mechanical pulp fiber. The fibers aretypically 0.1 to 2 microns in thickness and 10 to 400 microns in lengthand are additionally prepared according to U.S. Pat. No. 6,251,222,which is by this reference incorporated herein.

DETAILED DESCRIPTION OF THE INVENTION

[0023] Precipitation of PCC with Varying Morphologies

[0024] Continuous Flow Stir Tank Reactor (CFSTR)

[0025] Scalenohedral Morphology

[0026] The first step in this process involves making a high reactiveCa(OH)₂ milk-of-lime slake and screening it at −325 mesh. This slake isthen added to an agitated reactor, brought to a desired reactiontemperature, 0.1 percent citric acid is added to the slake to inhibitaragonite formation, and reacted with CO₂ gas. The reaction proceeds 10percent to 40 percent of the way through at which point the reaction isstopped. This produces a partially converted Ca(OH)₂/CaCO₃ slurry(approximately 20 percent solids by weight) which is then fed into areaction vessel at a rate that matches CO₂ gassing to maintain a givenconductivity (ionic saturation) to produce a scalenohedral crystal. Thisreaction proceeds until stabilization of the process is achieved. Theproduct made once stabilization is achieved (approximately 95 percentconverted) is then mixed with diluted fibers (approximately 1.5 percentconcentration) and water. This mixture is then reacted with CO₂ gas toendpoint pH 7.0. The product manufactured using this method can containfrom about 0.2 percent to about 99.8 percent scalenohedral PCC withrespect to fibers at 3 percent to 5 percent total solids.

[0027] The product has a specific surface area from about 5 meterssquared per gram to about 11 meters squared per gram; product solidsfrom about 3 percent to about 5 percent and a PCC content from about 0.2percent to about 99.8 percent, and is predominantly scalenohedral inmorphology.

[0028] Aragonitic Morphology

[0029] The first step in this process involves making a high reactive Ca(OH)₂ milk-of-lime slake and screened at −325 mesh. The concentration ofthis slake is approximately 15 percent by weight. This slake is thenadded to an agitated reactor, brought to a desired reaction temperature,from about 0.05 percent to about 0.04 percent additive is added todirect morphology and size, and reacted with CO₂ gas. The reactionproceeds 10 percent to 40 percent of the way through at which point thereaction is stopped. This produces a partially converted Ca (OH)₂/CaCO₃slurry which is then fed into a reaction vessel at a rate that matchesCO₂ gassing to maintain a given conductivity (ionic saturation) toproduce an acicular, aragonitic crystal. The reaction continues untilprocess stabilization is achieved. The product made once stabilizationis achieved, (approximately 95 percent calcium carbonate) is mixed withdiluted fibers (approximately 1.5 percent concentration) and water. Thecalcium carbonate and fibers are then reacted with CO₂ gas to anendpoint of pH 7.0. The product manufactured using this method containsfrom about 0.2 percent to about 99.8 percent aragonitic PCC with respectto the fibers at about 3 percent to about 5 percent total solids.

[0030] The product has a specific surface area of about 5 meters squaredper gram to about 8 meters squared per gram; product solids from about 3percent to about 5 percent by weight and a PCC content from about 0.2percent to about 99.8 percent with respect to fibers and has apredominantly aragonitic morphology.

[0031] Rhombohedral Morphology

[0032] The first step in this process involves making a high reactive Ca(OH)₂ milk-of-lime slake which is screened at −325 mesh and has aconcentration of approximately 20 percent by weight. 0.1 percent citricacid is added to inhibit aragonite formation. A portion of this slake isadded to an agitated reactor, brought to a desired reaction temperatureand carbonated with CO₂ gas. The reaction proceeds to conductivityminimum producing a “heel”. A “heel” is defined as a fully convertedcalcium carbonate crystal with average particle size typically in therange of about 1 micron to about 2.5 micron with any crystal morphology.Sodium carbonate is added to the remainder of the slake not used in themanufacture of the “heel” material. This slake and CO₂ is added to the“heel” material at a CO₂ gassing rate to maintain a given conductivity(ionic saturation) to produce a rhombohedral crystal. The reaction iscontinued until process stabilization is achieved. Once stabilization isachieved, this product (approximately 90 percent to 95 percentconverted) is mixed with diluted fibers (approximately 1.5 percentconcentration) and water. Additional CO₂ is added to an endpoint of pH7.0. The product manufactured using this method contains from about 0.2percent to about 99.8 percent rhombohedral PCC with respect to fibersand is about 3 percent to about 5 percent total solids.

[0033] The product has a specific surface area from about 5 meterssquared per gram to about 8 meters squared per gram; product solids fromabout 3 percent to about 5 percent; and PCC content from about 0.2percent to about 99.8 percent and has a predominantly rhombohedralmorphology:

EXAMPLES

[0034] The following examples are intended to exemplify the inventionand are not intended to limit the scope of the invention.

Example 1

[0035] Scalenohedral PCC

[0036] Reacted 15 liters of water with 3 kilogram CaO at 50 degreesCelsius producing a 20 percent by weight Ca(OH)₂ slake. The Ca(OH)₂slake was then screened at −325 mesh producing a screened slake that wastransferred to a first 30-liter double jacketed stainless steel reactionvessel with an agitation of 615 revolutions per minute (rpm). 0.1percent citric acid, by weight of total theoretical CaCO₃ to beproduced, was added to the screened slake in a 30-liter reaction vesseland the temperature of the contents brought to 40 degrees Celsius. Beganaddition of 20 percent CO₂ gas in air (14.83 standard liter minuteCO₂/59.30 standard liter minute air) to the 30-liter reaction vessel toproduce a 2:1 Ca (OH)₂/CaCO₃ slurry. At this point, CO₂ gassing wasstopped and the slurry was transferred to an agitated 20-liter storagevessel.

[0037] 2 liters of the 2:1 Ca(OH)₂/CaCO₃ slurry was transferred to afirst 4-liter agitated (1250 rpm) stainless steel, double jacketedreaction vessel. The temperature was brought to 51 degrees Celsius and20 percent CO₂ gas in air (1.41 standard liter minute CO₂/5.64 standardliter minute air) was added to the first 4-liter reaction vessel until apH of 7.0 was achieved producing a CaCO₃ slurry. Once a pH 7.0 wasachieved began addition of the 2:1 Ca(OH)₂/CaCO₃ slurry of the 20-literstorage vessel to the first 4-liter reaction vessel while continuing toadd 20 percent CO₂ gas in air (1.41 standard liter minute CO₂/5.64standard liter minute air) to the first 4-liter reaction vessel tomaintain a conductivity of approximately 90 percent ionic saturation.The addition of Ca(OH)₂/CaCO₃ slurry and CO₂ to the first 4-literreaction vessel was continued for approximately 12 hours until productphysical properties remained essentially unchanged, producing a CaCO₃slurry that was approximately 98 percent converted. Transferred 0.18liters of the 98 percent CaCO₃ slurry to a second 4-liter agitated (1250rpm), stainless steel, double jacketed reaction vessel, added 0.66liters of 3.8 percent by dry weight cellulosic fibers and diluted to 1.5percent consistency. This mixture of CaCO₃ slurry and fiber was reactedwith 20 percent CO₂ in air (1.41 standard liter minute CO₂/5.64 standardliter minute air) to produce a CaCO₃ filler-fiber composite. The calciumcarbonate filler had a predominantly scalenohedral morphology.

Example 2

[0038] Aragonitic PCC

[0039] Reacted 10.5 liters of water with 2.1 kilograms CaO at 50 degreesCelsius producing a 15 percent by weight Ca(OH)₂ slake. The Ca(OH)₂slake was then screened at −325 mesh producing a screened slake that wastransferred to a 30-liter double jacketed stainless steel reactionvessel with an agitation of 615rpm. Added 0.1 percent by weight of ahigh surface area (HSSA) aragonitic seed (surface area ˜40 meterssquared per gram, approximately 25 percent solids) to the 30-literreaction vessel and brought the temperature of the contents to 51degrees Celsius. A “seed” is defined as a fully converted aragoniticcrystal that has been endpointed and milled to a high specific surfacearea (i.e. greater than 30 meters squared per gram and typically aparticle size of 0.1 to 0.4 microns). Began addition of 10 percent CO₂gas in air (5.24 standard liter minute CO₂/47.12 standard liter minuteair) to the 30-liter stainless steel, double jacketed reaction vesselfor a 15-minute period after which the CO₂ concentration was increasedto 20 percent in air (10.47 standard liter minute CO₂/41.89 standardliter minute air) for an additional 15 minutes producing a 2.3:1 Ca(OH)₂/CaCO₃ slurry. At which time CO₂ gassing was stopped. The 2.3:1Ca(OH)₂/CaCO₃ slurry was transferred to an agitated 20-liter storagevessel. Transferred 2 liters of the 2.3:1 Ca(OH)₂/CaCO₃ slurry to afirst 4-liter agitated, double jacketed stainless steel reaction vesselwith agitation set at 1250rpm and the temperature was brought to 52degrees Celsius. Began addition of 20 percent CO₂ gas in air (1.00standard liter minute CO₂/3.99 standard liter minute air) to the first4-liter reaction vessel and the reaction was continued until a pH of 7.0was achieved producing a 100 percent CaCO₃ slurry. The temperature ofthe 100 percent CaCO₃ slurry of the first 4-liter reaction vessel wasbrought to 63 degrees Celsius. Began addition of the 2.3:1 Ca(OH)₂/CaCO₃slurry of the 20-liter storage vessel to the first 4-liter reactionvessel while continuing to add 20 percent CO₂ in air (1.00 standardliter minute CO₂/3.99 standard liter minute air) to the first 4-literreaction vessel maintaining a conductivity of approximately 90 percentionic saturation. Continued the reaction for approximately 9 hours untilthe physical properties of the resultant product remained essentiallyunchanged, producing a 98 percent by wt. CaCO₃ slurry.

[0040] Transferred 0.35 liters of the 98 percent CaCO₃ slurry to asecond 4-liter agitated (1250 rpm), stainless steel, double jacketedreaction vessel, added 0.66 liters of 3.8 percent by wt. cellulosicfiber and 1.0 liters water to the second 4-liter reactor producing a 1.5percent by wt. CaCO₃/fiber mixture. Added an additional 20 percent CO₂in air (1.00 standard liter minute CO₂/3.99 standard liter minute air)to the second 4-liter reaction vessel until a pH of 7.0 was reached atwhich time the reaction was completed producing a CaCO₃/fiber composite.The composite consisted of approximately 75 percent aragonitic PCC tofiber.

Example 3

[0041] Rhombohedral PCC

[0042] Reacted 15 liters of water with 3 kilograms CaO at 50 degreesCelsius producing a 20 percent by weight Ca(OH)₂ slake. The Ca(OH)₂slake was screened at −325 mesh producing a screened slake that wastransferred to an agitated 20-liter storage vessel. Transferred 2-litersof the screened slake from the 20-liter storage vessel to a first4-liter agitated, stainless steel, double jacketed reaction vessel andbegan agitation at 1250 rpm. Added 0.03 percent citric acid by weight oftheoretical CaCO₃ to the first 4-liter reaction vessel and raised thetemperature of the contents to 50 degrees Celsius. Added 20 percent CO₂gas in air (1.44 standard liter minute CO₂/5.77 standard liter minuteair) to the first 4-liter reaction vessel until a pH of 7.0 was achievedproducing a 100 percent CaCO₃ slurry. To the screened slake in the20-liter storage vessel, added a solution of 1.3 percent by weight ofNa₂CO₃, based on theoretical yield of CaCO₃, producing a Ca(OH)₂/Na₂CO₃slake. Increased the temperature of the contents of the first 4-literreaction vessel to approximately 68 degrees Celsius and began additionof the Ca(OH)₂/Na₂CO₃ slake of the 20-liter storage vessel to the first4-liter reaction vessel while continuing to add 20 percent CO₂ in air(1.44 standard liter minute CO₂/5.77 standard liter minute air) to thefirst 4-liter reaction vessel maintaining a conductivity ofapproximately 50 percent ionic saturation. Addition of theCa(OH)₂/Na₂CO₃ slake and CO₂ was continued for approximately 12 hoursuntil physical properties of the resultant product remained essentiallyunchanged producing an approximate 98 percent by wt. CaCO₃ slurry.

[0043] Transferred 0.22 liters of the 98 percent CaCO₃ slurry to asecond 4-liter agitated (1250 rpm) dual jacketed, stainless steelreaction vessel and added 0.66 liters of 3.8 percent by weightcellulosic fiber and 1.0 liters water to the second 4-liter reactorproducing a 1.5 percent by weight CaCO₃/fiber mixture. Added anadditional 20 percent CO₂ in air (1.44 standard liter minute CO₂/5.77standard liter minute air) to the second 4-liter reaction vessel until apH of 7.0 was reached at which time the reaction was completed producingan approximate 3.4 percent by wt CaCO₃/fiber composite. The calciumcarbonate had a predominantly rhombohedral morphology.

Example 4

[0044] Scalenohedral—CFSTR

[0045] Reacted 15 liters of water with 3 kilograms CaO at 48 degreesCelsius to produce a Ca(OH)₂ slake, added an additional 6 liters ofwater producing a 20 percent by weight Ca(OH)₂ slake. The 20 percentCa(OH)₂ slake was screened at −325 mesh and transferred to a 30-literdouble jacketed, stainless steel reaction vessel with an agitation of615rpm. Added 0.015 percent citric acid, by weight of total theoreticalCaCO₃ to be produced, to the 30-liter reaction vessel and thetemperature of the contents brought to 36 degrees Celsius. Beganaddition of 20 percent CO₂ gas in air (13.72 standard liter minuteCO₂/54.89 standard liter minute air) to the 30-liter reaction vessel toproduce a 5:1 Ca(OH)₂/CaCO₃ slurry. CO₂ gassing was stopped and theCa(OH)₂/CaCO₃ slurry was transferred to an agitated 20-liter storagevessel.

[0046] In a 4-liter agitated storage vessel, combined 0.25 liters of theCa(OH)₂/CaCO₃ slurry with 0.66 liters of 3.8 percent by weight fibersand with 1.09 liters of water making a Ca(OH)₂/CaCO₃/fiber material.Transferred 2 liters of the Ca(OH)₂/CaCO₃/fiber material to a 4-literagitated (1250 revolutions per minute) reaction vessel and thetemperature brought to 55 degrees Celsius and carbonated with 20 percentCO₂ in air (1.30 standard liter minute CO₂/5.23 standard liter minuteair) to a pH of 7.0 producing a CaCO₃/fiber composite. Prepared16-liters of 1.5 percent by weight fibers and a separate 10-liter vesselof water. To the 4-liter reaction vessel began addition of theCa(OH)₂/CaCO₃ slurry of the 20-liter agitated storage vessel, along withthe 1.5 percent consistency fiber mixture at 172.05 ml per minute, alongwith 31.21 ml per minute of additional water while maintaining the flowof CO₂ gas (1.30 standard liter minute CO₂/5.23 standard liter minuteair) at a rate to maintain conductivity of approximately 90 percentionic saturation, while maintaining mass balance of approximately 4percent to 5 percent total solids.

[0047] This reaction was continued until product physical propertiesremained essentially unchanged. Addition of material from the storagevessel was stopped while CO₂ addition was continued and the material inthe 4-liter agitated reaction vessel was brought to a pH of 7.0 at whichtime CO₂ addition was stopped producing a 2.2:1 CaCO₃/fiber compositewith the CaCO₃ having a well defined scalenohedral morphology.

Example 5

[0048] Scalenohedral CFSTR/Surfactant

[0049] Reacted 15 liters of water with 3 kilograms CaO at 48 degreesCelsius to produce a Ca(OH)₂ slake, added an additional 6 liters ofwater producing a 20 percent by weight Ca(OH)₂ slake. The 20 percentCa(OH)₂ slake was screened at −325 mesh and transferred to a 30-literreaction vessel (615 revolutions per minute). Added 0.015 percent citricacid, by weight of total theoretical CaCO3 to be produced, to the30-liter reaction vessel and the temperature of the contents brought to35 degrees Celsius. Began addition of 20 percent CO₂ gas in air (14.08standard liter minute CO₂/56.30 standard liter minute air) to the30-liter reaction vessel producing a 5:1 Ca(OH)₂/CaCO₃ slurry. At thispoint, CO₂ gassing was stopped and the Ca(OH)₂/CaCO₃ slurry wastransferred to a 20-liter agitated storage vessel.

[0050] In a 4-liter agitated storage vessel, combined 0.25 liters of theCa(OH)₂/CaCO₃ slurry with 0.66 liters of 3.8 percent by weight fibersand with 1.09 liters of water making 2 liters of Ca(OH)₂/CaCO₃/fibermaterial.

[0051] Transferred 2 liters of the Ca(OH)₂/CaCO₃/fiber material to a4-liter stainless steel, double jacketed, agitated (1250 revolutions perminute) reaction vessel and the temperature was brought to 58 degreesCelsius. Reacted the Ca(OH)₂/CaCO₃/fiber material with 20 percent CO₂ inair (1.30 standard liter minute CO₂/5.23 standard liter minute air) to apH of 7.0.

[0052] At this point, prepared 16-liters of 1.5 percent by weight fibers(6.32 liters of fibers at 3.8 percent consistency and 9.68 liters ofwater) and a separate 10-liter vessel of water. Added 0.04 percentsurfactant based on the volume of fibers at 1.5 percent consistency. Thesurfactant is Tergitol™ MIN-FOAM 2× which is available commercially fromUnion Carbide, 39 Old Ridgebury Road, Danbury, Conn. 06817.

[0053] Once a pH of 7.0 was achieved in the 4-liter reaction vessel,began addition of the remaining 5:1 Ca(OH)₂/CaCO₃ slurry from the20-liter agitated storage vessel, with a flow of the 1.5 percent fibermixture at 176.48 ml per minute and with 32.00 ml per minute water fromthe 10-liter vessel to the 4-liter reaction vessel while maintaining theflow of CO₂ gas (1.30 standard liter minute CO₂/5.23 standard literminute air) at a rate to maintain conductivity of approximately 90percent ionic saturation, while maintaining mass balance ofapproximately 4 percent to 5 percent total solids. Continued addition ofthe material from the agitated storage vessel to the reaction vesseluntil product physical properties remained essentially unchanged. Atwhich point, addition of material from the storage vessel was stoppedwhile CO₂ addition was continued to a pH of 7.0 at which time CO₂addition was stopped. This produced a 2.33:1 CaCO₃/fiber composite withthe calcium carbonate having a well defined scalenohedral morphology.

Example 6

[0054] Scalenohedral CFSTR/Polyacrylamide

[0055] Reacted 15 liters of water with 3 kilograms CaO at 48 degreesCelsius producing a Ca(OH)₂ slake, added an additional 6 liters of waterproducing a 20 percent by weight Ca(OH)₂ slake. The 20 percent Ca(OH)₂slake was then screened at −325 mesh producing a screened slake that wastransferred to a 30-liter agitated (615 rpm) reaction vessel. Added 0.1percent citric acid, by weight of total theoretical CaCO₃ to beproduced, to the 30-liter reaction vessel and the temperature of thecontents brought to 50 degrees Celsius. Began addition of 20 percent CO₂gas in air (15.01 standard liter minute CO₂/60.06 standard liter minuteair) to the 30-liter reaction vessel producing a 5:1 Ca(OH)₂/CaCO₃slurry. CO₂ gassing was stopped and the slurry was transferred to a20-liter agitated storage vessel. To a 4-liter agitated vessel added0.31 liters of the Ca(OH)₂/CaCO₃ slurry, 0.60 liters of fibers at 3.8percent consistency and 1.09 liters of water to produce aCa(OH)₂/CaCO₃/fiber material. 2 liters of the Ca(OH)₂/CaCO₃/fibermaterial was transferred to a 4-liter agitated (1250 revolutions perminute) reaction vessel and the temperature was brought to 51 degreesCelsius. Began addition of 20 percent CO₂ in air (1.34 standard literminute CO₂/5.34 standard liter minute air) until a pH of 7.0 was reachedproducing a CaCO₃/fiber composite.

[0056] At this point, prepared 16-liters of 1.5 percent by weight fibers(6.32 liters of fibers at 3.8 percent consistency and 9.68 liters ofwater) and a separate 10-liter vessel of water. Added 0.05 percentcationic polyacrylamide (Percol 292) based on the volume of fibers at1.5 per cent consistency. Percol 292 is commercially available fromAllied Colloids, 2301 Wilroy Road, Suffolk, Va. 23434.

[0057] Once a pH of 7.0 was achieved in the 4-liter reaction vessel,began addition of the remaining 5:1 Ca(OH)₂/CaCO₃ slurry from the20-liter agitated storage vessel, with a flow of the 1.5 percent fibermixture at 90 ml per minute, along with 48.5 ml per minute of additionalwater to the 4-liter agitated, double jacketed reaction vessel whilemaintaining the flow of CO₂ gas (1.30 standard liter minute CO₂/5.23standard liter minute air) at a rate to maintain conductivity level ofapproximately 90 percent ionic saturation, and maintain mass balance ofthe reaction to maintain product concentration at approximately 4percent to 5 percent solids. Continued addition of the material from theagitated storage vessel to the reaction vessel until product physicalproperties remained essentially unchanged. Addition of material from the20-liter storage vessel was stopped while CO₂ addition was continueduntil a pH of 7.0 was reached at which time CO₂ addition was stoppedproducing a 3.34:1 CaCO₃/fiber composite with the PCC having a welldefined scalenohedral morphology.

[0058] The control fiber of the present invention was refined at theEmpire State Paper Research Institute (ESPRI) using an Escher-Wyss(conical) refiner to an 80° SR (freeness). Measured by a fiber qualityanalyzer (using arithmatic means) the control fiber measured 200-400microns

[0059] How Control Filler-Fiber was Made

[0060] Produce a 15% solids slake and mix with fibers (˜1.5%consistency) React in the presence of CO₂ to endpoint of pH of 7.0producing a filler-fiber composite with a surface area of 6-11 m2/g (˜60to 80% PCC but can have more or less in composite) TABLE 1 BreakingLength Physical Properties in Meters Filler Loading ScalenohedralAragonitic Rhombohedral Control Levels Filler-fiber Filler-fiberFiller-fiber Filler-fiber 20 4,021 4,599 4,312 4,245 25 3,799 4,3583,813 3,715 30 3,280 3,674 3,871 2,998

[0061] TABLE 2 Tensile Strength Physical Properties in kN/m FillerLoading Scalenohedral Aragonitic Rhombohedral Control LevelsFiller-fiber Filler-fiber Filler-fiber Filler-fiber 20 3.062 3.555 3.3973.382 25 3.124 3.324 2.999 3.021 30 2.658 2.785 3.005 2.448

[0062] TABLE 3 Internal Bond Strength Physical Properties in ft-lbFiller Loading Scalenohedral Aragonitic Rhombohedral Control LevelsFiller-fiber Filler-fiber Filler-fiber Filler-fiber 20 237.70 264.07283.13 255.67 25 263.20 285.95 251.65 256.95 30 242.63 248.60 273.65249.53

[0063] The morphology controlled filler-fiber composite showedequivalent or greater physical properties (i.e. tensil strength,breaking length, and internal bond strength) as compared with thecontrol filler-fiber. TABLE 4 ISO Opacity Optical Properties FillerLoading Scalenohedral Aragonitic Rhombohedral Control LevelsFiller-fiber Filler-fiber Filler-fiber Filler-fiber 20 89.20 88.20 87.3888.18 25 89.93 89.15 88.78 89.55 30 90.95 90.40 89.68 90.83

[0064] TABLE 5 Pigment Scatter Optical Properties Filler LoadingScalenohedral Aragonitic Rhombohedral Control Levels Filler-fiberFiller-fiber Filler-fiber Filler-fiber 20 60.15 55.47 55.08 58.55 2564.90 62.40 61.10 65.40 30 70.55 69.55 65.80 73.13

[0065] The morphology controlled filler-fiber composite showedequivalent optical properties (i.e. ISO Opacity and Pigment Scatter) ascompared with the control filler-fiber.

We claim:
 1. A filler-fiber composite comprising: (a) feeding slakecontaining citric acid to a first stage reactor (b) reacting the slakecontaining citric acid in the first stage reactor in the presence ofcarbon dioxide to produce a first partially converted calcium hydroxidecalcium carbonate slurry (c) reacting the first partially convertedcalcium hydroxide calcium carbonate slurry in a second stage reactor inthe presence of carbon dioxide to produce a second partially convertedcalcium hydroxide calcium carbonate slurry and (d) reacting the secondpartially converted calcium hydroxide calcium carbonate slurry in athird stage reactor in the presence of carbon dioxide and fibrils toproduce a filler-fiber composite.
 2. The filler-fiber composite of claim1 wherein the fiber is from about 0.1 microns to about 2 microns inthickness and from about 10 microns to about 400 microns in length. 3.The filler-fiber composite of claim 2 wherein the filler isscalenohedral having a specific surface area of from about 5 meterssquared per gram to about 11 meters squared per gram.
 4. Thefiller-fiber composite of claim 3 wherein the calcium hydroxide calciumcarbonate slurry is converted from about 20 percent to about 40 percent.5. The filler-fiber composite of claim 4 wherein the first partiallyconverted calcium hydroxide calcium carbonate slurry is converted fromabout 41 percent to about 99 percent.
 6. The filler-fiber composite ofclaim 5 wherein the second partially converted calcium hydroxide calciumcarbonate slurry is converted to a filler-fiber composite.
 7. A methodfor producing a filler-fiber composite comprising: (a) feeding slakecontaining citric acid to a first stage reactor (b) reacting the slakecontaining citric acid in the first stage reactor in the presence ofcarbon dioxide to produce a first partially converted calcium hydroxidecalcium carbonate slurry (c) reacting the first partially convertedcalcium hydroxide calcium carbonate slurry in a second stage reactor inthe presence of carbon dioxide to produce a second partially convertedcalcium hydroxide calcium carbonate slurry and (d) reacting the secondpartially converted calcium hydroxide calcium carbonate slurry in athird stage reactor in the presence of carbon dioxide and fibers toproduce a filler-fiber composite.
 8. The method of producing thefiller-fiber composite of claim 7 wherein the fiber is from about 0.1microns to about 2 microns in thickness and from about 10 microns toabout 400 microns in length.
 9. The method of producing the filler-fibercomposite of claim 8 wherein the filler is scalenohedral and has aspecific surface area of from about 5 meters squared gram to about 11meters squared per gram.
 10. The method of producing the filler-fibercomposite of claim 9 wherein the calcium hydroxide calcium carbonateslurry is converted from about 20 percent to about 40 percent.
 11. Themethod of producing the filler-fiber composite of claim 10 wherein thefirst partially converted calcium hydroxide calcium carbonate slurry isconverted from about 41 percent to about 99 percent.
 12. Thefiller-fiber composite of claim 11 wherein the second partiallyconverted calcium hydroxide calcium carbonate slurry is converted to afiller-fiber composite.
 13. The filler-fiber composite of claim 1utilized in paper or paperboard
 14. The filler-fiber composite of claim7 utilized in paper or paperboard.
 15. The paper produced utilizing thefiller-fiber of claim
 1. 16. The paper produced utilizing thefiller-fiber of claim
 7. 17. A filler-fiber composite comprising: (a)feeding slake containing citric acid to a first stage reactor (b)reacting the slake containing citric acid in the first stage reactor inthe presence of carbon dioxide to produce a first partially convertedcalcium hydroxide calcium carbonate slurry (c) taking a first portion ofthe partially converted calcium hydroxide calcium carbonate slurryadding fibrils and reacting such in a second stage reactor in thepresence of carbon dioxide to produce a calcium carbonate\fibrilcomposite to serve as a heel and (d) taking a second portion of thepartially converted calcium hydroxide calcium carbonate slurry addingfibrils and surfactant and reacting in the presence of CO2 to produce asecond partially converted Ca(OH)2/CaCO3/fibril material and (e)reacting the second partially converted Ca(OH)2/CaCO3/fibril material inthe presence of CO2 in a third stage reactor to produce a filler-fibercomposite.
 18. The filler-fiber composite of claim 17 wherein the fiberis from about 0.1 microns to about 2 microns in thickness and from about10 microns to about 400 microns in length.
 19. The filler-fibercomposite of claim 18 wherein the filler is scalenohedral having aspecific surface area of from about 5 meters squared per gram to about11 meters squared per gram.
 20. The filler-fiber composite of claim 19wherein the calcium hydroxide calcium carbonate slurry is converted fromabout 20 percent to about 40 percent.
 21. The filler-fiber composite ofclaim 20 wherein the first partially converted calcium hydroxide calciumcarbonate slurry is converted from about 41 percent to about 99 percent.22. The filler-fiber composite of claim 21 wherein the second partiallyconverted calcium hydroxide calcium carbonate slurry is converted to afiller-fiber composite.
 23. A method for producing a filler-fibercomposite comprising: (a) feeding slake containing citric acid to afirst stage reactor (b) reacting the slake containing citric acid in thefirst stage reactor in the presence of carbon dioxide to produce a firstpartially converted calcium hydroxide calcium carbonate slurry (c)taking a first portion of the partially converted calcium hydroxidecalcium carbonate slurry adding fibrils and reacting such in a secondstage reactor in the presence of carbon dioxide to produce a calciumcarbonate\fibril composite to serve as a heel and (d) taking a secondportion of the partially converted calcium hydroxide calcium carbonateslurry adding fibrils and surfactant and reacting in the presence of CO2to produce a second partially converted Ca(OH)2/CaCO3/fibril materialand reacting the second partially converted Ca(OH)2/CaCO3/fibrilmaterial in the presence of CO2 in a third stage reactor to produce afiller-fiber composite.
 24. The method for producing filler-fibercomposite of claim 23 wherein the fiber is from about 0.1 microns toabout 2 microns in thickness and from about 10 microns to about 400microns in length.
 25. The method for producing filler-fiber compositeof claim 24 wherein the filler is scalenohedral having a specificsurface area of from about 5 meters squared per gram to about 11 meterssquared per gram.
 26. The method for producing filler-fiber composite ofclaim 25 wherein the calcium hydroxide calcium carbonate slurry isconverted from about 20 percent to about 40 percent.
 27. The method forproducing filler-fiber composite of claim 26 wherein the first partiallyconverted calcium hydroxide calcium carbonate slurry is converted fromabout 41 percent to about 99 percent.
 28. The method for producingfiller-fiber composite of claim 27 wherein the second partiallyconverted calcium hydroxide calcium carbonate slurry is converted to afiller-fiber composite.
 29. The filler-fiber composite of claim 17utilized in paper or paperboard
 30. The filler-fiber composite of claim23 utilized in paper or paperboard.
 31. The paper produced utilizing thefiller-fiber of claim
 17. 32. The paper produced utilizing thefiller-fiber of claim
 23. 33. A filler-fiber composite comprising: (a)feeding slake containing citric acid to a first stage reactor (b)reacting the slake containing citric acid in the first stage reactor inthe presence of carbon dioxide to produce a first partially convertedcalcium hydroxide calcium carbonate slurry (c) taking a first portion ofthe partially converted calcium hydroxide calcium carbonate slurryadding fibrils and reacting such in a second stage reactor in thepresence of carbon dioxide to produce a calcium carbonate/fibrilcomposite to serve as a heel and (d) taking a second portion of thepartially converted calcium hydroxide calcium carbonate slurry addingfibrils and polyacrylamide and reacting in the presence of CO₂ toproduce a second partially converted Ca(OH)₂/CaCO₃/fibril material and(e) reacting the second partially converted Ca(OH)₂/CaCO₃/fibrilmaterial in the presence of CO₂ in a third stage reactor to produce afiller/fiber composite.
 34. The filler-fiber composite of claim 33wherein the fiber is from about 0.1 microns to about 2 microns inthickness and from about 10 microns to about 400 microns in length. 35.The filler-fiber composite of claim 34 wherein the filler isscalenohedral having a specific surface area of from about 5 meterssquared per gram to about 11 meters squared per gram.
 36. Thefiller-fiber composite of claim 35 wherein the calcium hydroxide calciumcarbonate slurry is converted from about 20 percent to about 40 percent.37. The filler-fiber composite of claim 36 wherein the first partiallyconverted calcium hydroxide calcium carbonate slurry is converted fromabout 41 percent to about 99 percent.
 38. The filler-fiber composite ofclaim 37 wherein the second partially converted calcium hydroxidecalcium carbonate slurry is converted to a filler-fiber composite.
 39. Amethod of producing a filler-fiber composite comprising: (a) feedingslake containing citric acid to a first stage reactor (b) reacting theslake containing citric acid in the first stage reactor in the presenceof carbon dioxide to produce a first partially converted calciumhydroxide calcium carbonate slurry (c) taking a first portion of thepartially converted calcium hydroxide calcium carbonate slurry addingfibrils and reacting such in a second stage reactor in the presence ofcarbon dioxide to produce a calcium carbonate\fibril composite to serveas a heel and (d) taking a second portion of the partially convertedcalcium hydroxide calcium carbonate slurry adding fibrils andpolyacrylamide and reacting in the presence of CO₂ to produce a secondpartially converted Ca(OH)₂/CaCO₃/fibril material and (e) reacting thesecond partially converted Ca(OH)₂/CaCO₃/fibril material in the presenceof CO₂ in a third stage reactor to produce a filler/fiber composite. 40.The method for producing filler-fiber composite of claim 39 wherein thefiber is from about 0.1 microns to about 2 microns in thickness and fromabout 10 microns to about 400 microns in length.
 41. The method forproducing filler-fiber composite of claim 40 wherein the filler isscalenohedral having a specific surface area of from about 5 meterssquared per gram to about 11 meters squared per gram.
 42. The method forproducing filler-fiber composite of claim 41 wherein the calciumhydroxide calcium carbonate slurry is converted from about 20 percent toabout 40 percent.
 43. The method for producing filler-fiber composite ofclaim 42 wherein the first partially converted calcium hydroxide calciumcarbonate slurry is converted from about 41 percent to about 99 percent.44. The method for producing filler-fiber composite of claim 43 whereinthe second partially converted calcium hydroxide calcium carbonateslurry is converted to a filler-fiber composite.
 45. The filler-fibercomposite of claim 33 utilized in paper or paperboard
 46. Thefiller-fiber composite of claim 39 utilized in paper or paperboard. 47.The paper produced utilizing the filler-fiber of claim
 33. 48. The paperproduced utilizing the filler-fiber of claim 39.